Preparation

Set a buttered 5-6 cup soufflé dish or other straight-sided baking dish in a larger baking pan that is at least 2 inches deep; set aside.

In a deep bowl, beat egg whites with mixer on high until foamy. Gradually beat in ¼ cup of the sugar; continue to beat until whites hold short, distinct peaks. Set aside.

In another bowl, combine butter, remaining ½ cup sugar, lemon zest, and egg yolks. Beat on high until mixture is thick and lighter in color. Stir in buttermilk, lemon juice, and flour. Add about a fourth of the egg whites to batter, stir to mix well. Gently but thoroughly fold in remaining whites.

Pour batter into soufflé dish. Set dish (in baking pan) in middle rack of a 350 degree oven. Pour boiling water into baking pan up to level of batter. Bake until top of pudding is a rich brown and center feels firm when lightly pressed (about 1 hour).